1. Field of the Invention
This invention relates to communication and routing in a redundant network topology, and more particularly to a multi-ring network and method using autonomous instances of an interior gateway protocol (IGP).
2. Description of the Related Art
Internet protocol (IP) multicast is a technique for one-to-many communication over an IP infrastructure in a network. IP multicast scales to a larger receiver population by not requiring prior knowledge of who or how many receivers there are. Multicast uses network infrastructure efficiently by requiring the source to send a packet only once, even if that packet needs to be delivered to a large number of receivers. The nodes (routers) in the network take care of replicating the packet to reach multiple receivers only when necessary.
An IP multicast group address is used by sources and receivers to send and receive content. Sources use the group address as the IP destination address in their data packets. Receivers use this group address to inform the network that they are interested in receiving packets sent to that group. For example, if some content is associated with group address 239.1.1.1, the source will send data packets destined to 239.1.1.1. Intended receivers of that content will “join” the IP multicast group, informing the network that they are interested in receiving data packets sent to the group address 239.1.1.1. The protocol used by receivers to join a group is called the Internet Group Management Protocol (IGMP).
Once the receivers join a particular IP multicast group, an IP multicast distribution tree is constructed for that group. The protocol most widely used for this is Protocol Independent Multicast (PIM). It sets up multicast distribution trees such that data packets from senders to a multicast group reach all receivers that have joined the group. For example, all data packets sent to the group address 239.1.1.1 are received by receivers who joined group address 239.1.1.1. The multicast tree construction is initiated by network nodes which are close to the receivers, i.e. it is receiver driven. As PIM join requests traverse the nodes in the network back to the source, each node (router) adds to the construction of the distribution tree. At each node, the router determines the next best hop (node) to eventually reach the source. As a consequence, the path from the source to the destination receiver is the shortest path.
The network of routers implements an instance of an Interior Gateway Protocol (IGP) such as IS-IS to determine the next best hop (node) to reach the source destination. The IGP instance configures each router with any interfaces and sources that are directly connected to each router. The routers share information regarding which sources are directly connected to which routers. Each router then constructs an IGP Table that lists the next-hop interface and next hop for each source in the network. The routers share information regarding the topology of the network, so that the constructed path in the distribution tree from any source to any destination receiver is the shortest possible path. The network is set up if all of the routers are working properly. When a router receives an IGMP join from a receiver or a PIM join from another node, the router looks up the next hop (node) for the source destination and forwards the PIM join. At each node, a branch is added up the tree until reaching the root (i.e. the source destination).
Each host (and each application on the host) that wants to be a receiving member of a multicast group (i.e. receive data corresponding to a particular multicast address) must send an IGMP join request. Adjacent routers use a PIM join to forward the initial join request from node-to-node to the source. In multicast routing, the source address is used to determine data stream direction. The source of the multicast traffic is considered upstream. The router determines which downstream interfaces are destinations for this multicast group (the destination address), and sends the packet out through the appropriate interfaces. The term “reverse path forwarding” is used to describe this concept of routing packets away from the source, rather than towards the destination.
A “ring” network is a network topology in which each ring node connects to exactly two other ring nodes, forming a single continuous pathway for signals through each node—a ring. Data travels from node to node, with each node along the way handling every packet. Many ring networks add a “counter-rotating ring” to form a redundant topology. The routers connected at the nodes in the ring are referred to as “core routers”. These routers will typically connect to the receivers and sources via one or more distribution and access routers. IGP exists throughout all of the core, access and distribution routers throughout the network. An IGP Table provides the next hop and the next hop interface, which is what each node uses in order to route a packet to a particular destination. The core router independently decides whether to use the clock wise or anti-clockwise ring to reach the node.